Shades or blinds of the accordion type, such as those made of a pleated fabric or hexagonal cell structure are in increasingly widespread use particularly in acting as closures across skylights or clerestory windows installed in commercial and residential buildings. Such architectural elements provide natural sunlight as well as passive solar heating or ventilating to an occupied space. However, fenestration controls using the standard pleated or hexagonal cell-type shades have not been completely satisfactory for such out-of-reach windows. In the past, the fenestration controls employed have included a motorized system where the fabric or cords are wound upon a drum, a manual system where the shade is opened or closed by hand or through the use of a rod or pole, or merely to use a fixed-in-place shade that cannot be opened.
In the foregoing and other applications, it is important that the shade assembly be of lightweight, compact construction which requires the least number of parts, can be easily installed while being adjustable for different length openings and capable of automatically compensating for differences in tension on opposite sides of the shade or blind as well as to prevent overloading of the motor drive when the shade is driven into the closed position.
Of the various approaches taken in the past, U.S. Pat. No. 4,368,770 to T. Ulfhielm employs an electric motor and two gears to wind up a cable in retracting collapsible shades or panels. U.S. Pat. No. 4,212,341 to E. V. Fisher employs parallel cords on rollers above and below the blind itself, the cords being elastic in order to reduce any stress in the system. U.S. Pat. No. 4,202,395 to R. A. Heck et al also employs pulleys on parallel cords above and below the blind itself and provides for spring-loading to maintain a constant line tension. U.S. Pat. No. 3,646,877 to D. H. Ellis discloses a worm gear drive for a cable drum system, and similarly U.S. Pat. No. 3,576,206 to P. C. Trexler winds up parallel cords on a motorized drum, and stationary pulleys are mounted at the two bottom corners of the opening. Other patents of interest are U.S. Pat. No. 2,874,612 to S. N. F. Luboshez; U.S. Pat. No. 3,465,806 to E. M. Sulkes; U.S. Pat. No. 3,665,996 and U.S. Pat. No. 3,752,208 to F. D. Roberts.